51吃瓜 of the Day
evection
noun
a periodic irregularity in the moon's motion, caused by the attraction of the sun.
More about evection
Evection, 鈥渁 periodic irregularity in the moon’s motion,鈥� comes from Latin 脓惫别肠迟颈艒 (stem 脓惫别肠迟颈艒n-) 鈥渁 going upwards, flight.鈥� 膾惫别肠迟颈艒 is based on the verb 脓惫别丑别谤别 鈥渢o carry forth, move forth,鈥� from 脓 (or ex) 鈥渙ut of, from, beyond鈥� and vehere 鈥渢o carry, drag.鈥� Vehere has two common stems in English: veh-, as found in vehement and vehicle, and vect-, as in convection and vector. Distant relatives of vehere in English include way, wagon, weigh, wiggle, and even Norway (literally 鈥渘orth way鈥�). Evection was first recorded in English in the 1650s.
how is evection used?
The point at which a moon and its planet come closest together, known as periapsis, is not constant …. When the period of this precession matches the time it takes the planet itself to orbit the sun, the sun鈥檚 gravity will distort the moon鈥檚 orbit. This is evection.
Jeremiah Horrocks[鈥檚] 鈥� life was short, but he accomplished a great deal, and rightly ascribed the lunar inequality called evection to variations in the value of the eccentricity and in the direction of the line of apses, at the same time correctly assigning the disturbing force of the Sun as the cause.
canicular
adjective
pertaining to the rising of the Dog Star (also called Sirius) or to the star itself.
More about canicular
Canicular, 鈥減ertaining to Sirius, the Dog Star,鈥� is equivalent to Latin 颁补苍墨肠耻濒补 鈥淪irius鈥� plus -腻谤颈蝉, an adjective-forming suffix. 颁补苍墨肠耻濒补 literally means 鈥渓ittle dog鈥� and is based on canis 鈥渄og,鈥� plus the feminine diminutive suffix -cula (compare English -cle or -cule, as in molecule and particle). Canis survives today as French chien, Italian cane, and Portuguese 肠茫辞, but Spanish can has declined in favor of perro, of unclear origin. A direct descendant of 颁补苍墨肠耻濒补 is French canicule 鈥渉eat wave,鈥� which previously referred to the dog days of summer. This period of the year takes its name in both English and Romance languages from the appearance of Sirius in the northern sky, and the co-occurrence with hot weather gives dog days as well as French canicule their heated sense. Canicular was first recorded in English in the late 14th century.
how is canicular used?
Sirius was then above the horizon during daylight hours, so it was believed the star鈥檚 heat was added to that of the Sun to give a run of scorching temperatures. The interval from early July to mid-August of Dante鈥檚 鈥済reat scourge of canicular days鈥� is still referred to as the dog days of summer in modern times.
鈥嬧�婲ow beat the pulse and burned the flame of that canicular time when Sirius, rising with the sun, adds his glow to the lesser planet for earth’s delight.
apastron
noun
the point at which the stars of a binary system are farthest apart.
More about apastron
Apastron, 鈥渢he point at which binary stars are farthest apart,鈥� is based on Ancient Greek 补辫贸 鈥渁way, off, apart鈥� and 谩蝉迟谤辞苍 鈥渟tar, constellation.鈥� 础辫贸, which remains apo- in English before most consonants (as in apology) but becomes ap- before vowels and h (as in aphorism). Distant relatives of 补辫贸, all featuring a telltale labial (using the lips) consonant, include English after and off, Latin ab 鈥渁way from,鈥� and Sanskrit 谩辫补 鈥渁way, off.鈥� 脕蝉迟谤辞苍 is based on 补蝉迟岣梤 鈥渟tar鈥� (compare the recent 51吃瓜s of the Day asterism and astronaut), which is a cognate and synonym of English star and Latin stella (compare the recent 51吃瓜s of the Day circumstellar and stellate). Apastron was first recorded in English in the early 1840s.
how is apastron used?
Owing to the great eccentricity of the orbits of double stars, such stars are anywhere from twice to nineteen times as near to each other at periastron as they are at “apastron,” or point of greatest departure.